In order to improve the efficiency of a fan, it is known to provide it on the upstream side with a fixed system of vanes called a distributor, or on the downstream side with fixed system of vanes called a corrector, so that the fluid which has been taken in without any rotation will also be discharged without any rotation, or without any appreciable rotation.
However the presence of this system entails disadvantages: firstly, it increases the cost of the fan, secondly, it causes a noise like a siren due to the periodic passage of the mobile blades of the fan in front of the fixed vanes of the distributor or of the corrector and lastly, it causes losses of head, however small they may be, by friction which is added to the losses of head of the second fluid on passing over the outside walls of the heat exchanger.
Preferred embodiments of the present invention mitigate these disadvantages.
The present invention provides an improvement to a system for heat exchange between a first fluid flowing inside ducts of a set of heat exchangers and a second fluid passing over the outside surfaces of the heat exchangers in a forced flow or assisted flow provided by a fan placed in a chimney downstream from the heat exchangers in relation to the flow direction of the second fluid, wherein the heat exchangers are placed at the bottom of and round the chimney and are so oriented that the streams of the second fluid emerging from the heat exchangers form on the average, in a plane perpendicular to the axis of rotation of the fan, an angle .alpha. with the local radii emanating from the meeting point of said axis with said perpendicular plane, said angle .alpha. being calculated so that during average operation of the assembly, the angular momentum of said second fluid in relation to the axis of the fan, at the output of the heat exchangers, is substantially equal but in the opposite direction to the angular momentum imparted to said second fluid by the rotation of the fan, such that the angular momentum resulting from the second fluid in relation to the axis of the fan will be close to zero at the output of the fan.
There has thus been produced as assisted flow heat exchange system in which the heat exchangers are also used, in addition to their heat exchange function, as distributors for the fan by means of a judicious orientation of the heat exchange elements.
Doing this requires one distributor less and hence the extra loss of head due to this distributor and the siren noise which it causes are minimised, while the advantage of a fan with a distributor which enables it to discharge the fluid without any rotation or without any appreciable rotation in the chimney is maintained, thus improving the efficiency.
According to a particular embodiment of the invention the heat exchangers are substantially horizontal finned tube heat exchangers and they are disposed round the chimney in such a way that the fins guide the fluid at said angle .alpha..
According to another embodiment of the invention the heat exchangers are vertical tube heat exchangers and are disposed so that a perpendicular drawn in the mid plane of the heat exchanger will form said angle .alpha. with the radius ending at the foot of this perpendicular.
According to another embodiment, the heat exchangers are disposed in pairs around the base of the chimney in such a way that a pair of heat exchangers will be contiguous along their vertical side, and the mid plane of the dihedral formed by the two heat exchangers will form said angle .alpha. with a local radius ending in the vicinity of the middle of the arc covered by the two heat exchangers.
According to another embodiment of the invention, the heat exchangers are disposed in pairs around the base of the chimney, each pair being composed by two heat exchangers of different dimensions disposed on two sides of a triangle whose third side is formed by a part of the periphery of the base of the chimney.